Ultra-sonic wave transducers



Jan. 29, 1957 MALHERBE I 2,779,880

ULTRA-SONIC WAVE TRANSDUCERS Filed March 18, 1952 2 Sheets-Sheet l P FLEXIBLE DIAPHRAGM Wally/0111114142 P/EZOELECTR/C' CL INVENTOR ATTORNEY Jan. 29, 1957 G. MALHERBE 2,779,880

ULTRA-SONIC WAVE TRANSDUCERS Filed March 18, 1952 2 Sheets-Sheet 2 -FigA-a INVENTOR 5 0 :5 Ma/berbe ATTO R N EY LTRA-some WAVE TRANSDUCERS V Georges Malherbe, Montigny le Tilleul, Belgium, as-

signor' to Ateliers de'Constructions Electriques dc Charleroi, Brussels, Belgiunn'a company of Belgium 1' .j Application March 18,1952, Serial N 277,330

- '14 Claims; (Cl.31 08.3)

""The present invention relates todevices intended to transmit elastic waves, an'd'particularly ultra-sonic waves;

from an emitter device to a 'body'to be examined or treated with these waves. f '7 These devices are commonly called ultra-sonicfwave transducers and the invention relates more particularly to'ultra-sonic transducers comprising-ajcontainer filled with a' wave-conducting liquid which is in contact both with the wave-emitting device, for example a piezo-electric crystal, and with a flexible wall of the container adapted to engage the body to be examined or treated.

One example of these ultra-sonic transducers has been described in prior patent application, Serial No. 684,614, now Patent No. 2,532,507 issued December 5, 1950 relating to turgescent feeler apparatus. Ultra-sonic wave transducers produced in the. form ofturgescent feelers generally work well and are in current use.

There are, however, cases of practical application where the turgescent feelers such as described in the said patent application are diflicu'lt, if not impossible, to use because of their large dimensions. r These ultra sonic wave transducers, as now constructed in the form of turgescent feelers, comprise a hollow body of cylindrical general shape, filled with a wave conducting liquid, the two ends being respectively closed by. a piezo-electric quartz crystal element capable of emitting ultra-sonic waves and by a flexible wall capable of bulging under the pressure of the filling liquid and of engaging snugly a portion of the surface of a body to beexamined'or treated, without any appreciable air gap between the two surfaces in contact. For reasons of directivity, i. e. concentration of the ultra-sonic waves into a relatively narrow beam in a given direction, and taking account of the wave-length of the emission, it has been found desirable to use an emitting device having a relatively largesurface, which entails a cylindrical container of correspondingly large -diameter.. This results in a transducer of considerable overall size and having a flexible wall of fairly large area at the outlet end. For example, in an ultra-sonic wave transducer which is currently manufactured, the diameter of the emitter device is about 20 mm. and the external diameter of the cylin drical container is about 40 mm. If account be taken of thearea lost in the mounting of the crystal, there is thus obtained a directivity along the axis of the container equal'to the theoretical directivity or" a vibrating surface about mm. in diameter. a In these conditions, it is easily understood that an ultra-sonic wave transducer having such dimensions cannot be employed in all cases of practical application. It is particularly unsuitable for exploring or treating a body having a surface that is difficult of access, as, for example, a body-having rectangular or trapezoidal grooves or recesses with a narrow entry area, less than 40 mm. in the case considered. L V A solution which comes immediately to mind in this Unite States Patent cylindrical member usually employed; The axis of the case is to use a transducer of smaller size, which can'be' introduced into the recesses so as'to secure proper contact between the bottom of a recess and the flexible wall of the transducer. That would involve the use as waveemitter of a piezo-electric crystal of smaller diameter, corresppnding to a very small effective vibrating .area, from which it follows that, for convenient excitation voltages and powers, the intensity of the radiations emitted would be verylow; Moreover, all other things being equal any reduction of the diameter of the vibrating.

surface leads to a great reduction of the directivity.

Another solution which might be considered consists in using, with a quartz crystal wave emitter of normal dimension, for example mm. diameter, a hollow supporting member of frusto-conical shape instead of the cone frustum being coincident with that of'the crystal,

. There would thus be obtained a radiation of suitable intensity with an exciting voltage and power which are admissible.

However, tests carried out upon-ultra-sonic Wave transducers constructed in this way show that, although the waves emitted by the crystal may be concentrated upon a small area at the opposite end of the cone frustum,

the energy emitted diverge widely at the outlet from" the cone. In a plane parallel to the emitter crystal, around a central zone of high transmitted energy, there is a zone of lower intensity surrounded by an annular area of high energy, the position and intensity of which differ-from those corresponding to the first diffraction ring provided by Huygens theory.

This arises from the fact that the part of the ultrasonic waves coming from the periphery of the piezo electric crystal is reflected by the walls of the cone and emerges from the latter at an angle to it axis. This angle can be calculated by the general laws of reflection in geometrical optics.

The present invention provides a wave .transducer of small dimensions at the place of contact with the body.

to be examined or treated and possessing a small outlet area, while not having the drawbacks pointed out above of the transducer with small emitting element or the transducer in the form of a convergent cone.

Moreparticularly the invention relates to an improvement in ultra-sonic wave transducers with liquid conducting medium, like the turgescent feelers described in theyaforesaid patent application, and consisting in the fact that the container enclosing the liquid conducting the ultra-sonic waves from the wave-emitter device to a body to be examined or treated. with the said waves 'comprises two hollow frusto-conical portions arranged coaxially and joined at their small bases, the two ends'of the convergent-divergent double cone frustum thus constituted being of different cross-sectional areas, the Waveemitting device being disposed normally to the axis'of the double cone frustum andat its larger end, and the smallerend of the double cone frustum, closed by a flexible wall, constituting the outlet for the ultra-sonic waves.

The invention is hereinafter described with reference to the accompanying drawings, in which:

. Fig. 1 represents diagrammatically an ultra-sonic wave transducer such as described-in the aforesaid patent application.

Fig. 1a is a graph of directivity of the transducer represented in Fig. l, as explained below.

Figs. 2. and 2a represent an ultra-sonic wave transducer Patented Jan. 29, 1957 inthe form of a convergent cone; and-its directivity Figs. 4 and '41; represent an ultra-sonic wave transducer according to the invention, having an interior profile in the form of a convergent-divergent double cone frustum, and its directivity graph.

Fig. '5 represents an example of the use of the .ultrasonic wave transducer according to the invention.

Fig. 6 represents another embodiment of the invention.

In Figs. 1 to 4, the character C designates wave-emitting means, e. g. a quartz crystal emitting ultra-sonic waves,

' E is the. container forming the body orh'ousi'ng of the transducer and containing. a liquid'for conducting the ultra-sonic waves, P indicates aflexible wall, made, for example, of rubber, closing the end of the housing opposite-"the'crystal C and intended to establish proper contact between the transducer and the body to be examined ortreated with the ultra-sonic waves.

Inthe embodiment of the invention illustrated in Fig. 4, the housing E of the transducer comprises two hollow frusto-conical portions E1 and E2 which have a common axis X. The small ends of the frusto-conica'l por: tions are of equal cross-section and are joined in a neck portion N. The large ends of the frusto-conical portions E1 and E2 are of unequal size, the large end 21 of portion E1 being larger than the large end eg of portion E2. The cross-section of the neck N is smaller than either of the ends e1 or e2 of the housing. Thus, proceeding from the large end 'er at which the emitting means C is located, the walls of the housing E first converge to the neck N and then diverge to the opposite end as of the housing which is closed by the'flexible wall P. However, the total amount of divergence is less than the total convergence so that the cross-sectional area of the end eg of the housing closed by the wall P is less than that of the end e1 Where the crystal C is located. This is achieved by having the housing portion Ez shorter than the portion E1 in an axial direction or by having the angle of the truncated cone forming the 7 portion E2 smaller than that forming the portion E1 or by a combination of both of these factors, It has been 7 found that good results are obtained when the ratio of the cone angle of portion E1 to that of portion E2 has a value between 1:1 and 2:1.

The directivity graphs of the transducers represented in. Figs; 1 to 4 are shown in Figs. la to 4a, respectively,

and have been obtained in the following manner: The

transducer and a receiver'of ultra-sonic waves were arranged in a medium conductive to the ultra-sonic waves, for example water, at a convenient distance from one another. The receiver, which was centered beforehand exactly on the axis of the emitter, was displaced along a straight line lying in a plane perpendicular to that axis. .At each position upon that straight line, the receiver was orientated accurately towards the emitter. There were then plotted'as ordinates upon the diagrams of Figs. 1a to 4a, the deflections of an apparatus measuring the energy transmitted to the receiver, as a function of the distance from the receiver to the axis of the emitter, this distance being measured inthc plane normal to the, axisand being plotted as abscissa.

The scales used were the same, both for abscissae and for ordinates, for all of the graphs shown in Figs. 1a to 4a, and all the measurements were effected with the same voltagefor excitation of the emitter device.

Lastly, the sectional area of the emitter device was the same for the transducers of Figs. 1, 3 and 4, while the outlet area for the ultra-sonic waves from the transducer was the same for the transducers of Figs. 2, 3 and 4.

Consideration of these figures shows clearly the advantage of the transducer represented in Fig. 4, both as regards directivity and as regards intensity of the. radiation emitted, over the transducers represented in Figs.

embodiment shown in Fig. 4 is equal to that of the houscrystal.

4 2 and 3. In the-case of Fig. 2, thesmall area of the emitter device results in a lower sensitivity of the crystal and in spacing of the first and second lateral maxirna, under Huygens theory, farther from the axis of the transducer. The inferior directivity of the transducer represented in Fig. 3 is due to the path followed by the portion of the wave emitted by theperipheral portion of the the emittedwave in thecase of Figs. 3 and 4 are shown. in broken lines and clearly illustrate the superior directivity of the wave transducer-according t0. the invention.

When thecone angle of the housing portion E2 of the ing portion E1, the paths of the waves reflected first by the. side walls of the portion E1 and then by the side walls of the portion E2 are parallel to one another. If the cone angle of the housing portion E2 is less than that of the housing portion E1, thepaths of the reflected waves in the peripheral portion of the housing are caused to converge and are'thereby focused.

Fig. 5 shows 'by way of example a practical applica tion ofthe improved transducer, where the transducer represented in Fig. 1 is not capable of being used. T designates a metallic body to be examined with the ultrasonic waves, this body being provided with a recess or notch L the width of which is less than the diameter of the transducer represented in Fig. 1, but of such size that it is possible to introduce the improved transducer into V ducer while the transducer shown in Fig. 1 cannot be used.

The foregoing description covers one embodiment of the improved wavetransducer, having a small surface for contact with the bodies to be. examined or treated with ultra-sonic waves, and its advantages over other types of transducers have been explained, these advantages consisting particularly in good directivity of the waves leaving the transducer and high intensity of radiation emitted in normal conditions of use, It is possible to obtain substantially the same results by using an ultrasonic wave transducer of modified shape and particularly a transducer of biparaboloidal internal profile according to a second embodiment of the invention.

In this embodiment of the invention, the ultra-sonic wave transducer, with liquid conducting medium, comprises two hollow paraboloids, aligned on the same axis, having the same focus and delimited by end sections perpendi cular to said axis, the principal parameters and the axial lengths of the two paraboloids being such that said end sections are of dilferent sizes, the two paraboloids axis at the larger of the delimiting end sections, and the smaller'ofthese end" sections being closed by a flexible wall constituting the outlet for the ultra-sonic waves. 7

Fig. 6 represents diagrammatically an, ultra-sonic wave transducer constructed, according to the invention, in the form of two coaxial paraboloids having the same focus, the transducer being shown schematically in section on a plane containing the common axis. The transducer comprises a piczo-eiectric crystal C emitting ultra-sonic waves, a container E intended to enclose the liquid conductive to these waves and comprising two paraboloids Pr and P2 and a flexible wall P for pressing upon the surface of a body to be examined or treated with the said waves. There is also, indicated at M a sleeve or neck portion'uniting the two paraboloids P1 and P2 constituting the container or enclosure E. v

It will be easily understood that it is possible to obtain by means of a wave transducer constructed in this way an optimum directivity of the emitted waves along the axis: of the. transducer, while having very small out let area and overall size. In fact, all the ultra-sonic The paths followed by the different portions of wayes emitted normally to the crystal C, except a small central portion corresponding in area to the cross-section of the neck M, are concentrated at the focus of the first paraboloid. As this focus is also that of the second paraboloid, the ultra-sonic waves will be reflected from the walls of the latter paraboloid and will finally leave the transducer parallel to the axis of this latter. The waves from the aforementioned small central area of the crystal pass straight through the neck portion M. It is possible to select the outlet area of the transducer as small as may be desired by adopting suitable values for the principal parameters and the axial lengths of the two para boloids, or of the two parabolae obtained by taking a Section of the paraboloids on a plane passing through their common axis.

The equation of a parabola relative to its axis and to its tangent at the apex being y =2px,' where p represents the principal parameter, it is possible, for example,

to obtain an outlet area of a diameter equal to half the effective diameter of the emitter element by adopting principal parameters 121, p2 and axial lengths L1, L2 satisfying the relation:

wherein the suffix 1 relates to the larger parabola P1 and the sufl'ix 2 to the smaller parabola P2. For example, the relations adopted might bez tion. However, in many cases, it is satisfactory to approximate this ideal form by simpler surfaces,.as, for ext'o-conical portions are approximationsof the ideal biparaboloidal profile such as that shown in Fig. '6 andhave been found to produce good results while being easier to manufacture;

While several forms of the invention have been illus- I trated and described, it will be understoodthat the invention is thus not limited to the specific embodiments shown by way of example in the drawings.

What I claim and desire to secure' by Letters Paten axiallywith their small ends communicating with one another :said housing being filled witha wave conducting medium, wave-emitting means closing the larger end of 1; Inan ultra-sonic wave transducer, a hollow hous ing comprising two frusto -conical portions disposed cofrom said emitting means are transmitted by said wave conducting medium and are in part reflected by said annular wall with a twofold reflection, once before and once after said section of reduced cross-sectional area so as to be focused into a beam of higher concentration and better directivity at the smaller end of said housing.

2. In an ultra-sonic wave transducer, a hollow housing comprising two frusto-conical portions having equal cross-section at their small ends and unequal cross-section at their large end, said frusto-conical portions being disposed coaxially with their small ends in communication with one another said housing being filled with a Wave conducting medium, wave-emitting means closing the larger end of the frusto-conical portion of larger cross-section and a flexible wall closing the opposite end of the housing, whereby waves from said emitting means are transmitted by said wave conducting medium and are in part reflected by said annular wall with a twofold reflection, once before and once after said section of reduced cross-sectional area so as to be focused into a beam of higher concentration and better directivity at the smaller end of said housing.

3. In an ultra-sonicwave transducer, a hollow hous ing comprising two hollow paraboloids disposed coaxially with one another and with their foci substantially coinciding and a neck portion connecting said paraboloids, said housing being filled with a wave conducting medium, wave-emitting means at one end of the housing and a flexible wall closing the opposite end of the housing, whereby waves from said emitting means are transmitted by said wave conducting medium and are in part reflected by said annular wall with a twofold reflection, once before and once after said section of reduced crosssectional area so, as to be focused into a beam of higher concentration and better directivity at the smaller end of said housing.

4. In an ultrasonic wave transducer, a hollow housing comprising two hollow paraboloid portions disposed coaxially with one another and with their foci substantially coinciding and a neck portion connecting said paraboloid portions, one of said paraboloid portions having a base of larger cross-section than the other, said housing being filled with a wave conducting medium wave-emitting means at the base of larger cross-section and a flexible wall closing the opposite end of the housing, whereby waves from said emitting means are transmitted by said wave conducting medium and are in part reflected by said annular wall with a twofold reflection, once before and once after said section of reduced cross-sectional area so as to be focused into a beam of higher concentration and better directivity at thesmaller end of said housing.

1 References Cited in the file of this patent UNITEDSTATES PATENTS V 2,503,831 -Mason Apr ll, 1950 2,532,507 Meunier Dec. 5, 1950 2,565,725 Frederick et a1 Aug. 28, 1951 2,632,634 Williams Mar. 24, 1953 2,668,529 Huter Feb. 9, 1954 r FOREIGN PATENTS:

745,611 France Feb. 21, 1933 

